The concept of reducing piston engine exhaust noise by controlling the flow through the exhaust line has been investigated theoretically and demonstrated experimentally in previous work. While this work demonstrated a successful application to a medium size diesel engine in fixed operational conditions, the issue of back pressure was not addressed. Back pressure can be mitigated by the interposition of a buffer volume, the size of which is a determining factor in system performance, particularly when it is designed to operate over a broad range of engine speed and loading. This paper presents a simplified model of an active flow control exhaust system, which is then applied using a 16 litres, 8 cylinder diesel engine, in order to estimate back pressure, control valve loading and dimension its key components in such a way that back-pressure is maintained below a specified threshold over a broad range of speed and loading.
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